The present invention relates to a tensioner for applying a constant tension on a timing chain or belt driving a camshaft of a motorcycle or automobile.
A belt or chain tensioner is used to maintain a constant tension on the belt or chain by tensioning in predetermined direction when the belt or chain is slackened by elongation or wear during operation.
A conventional belt tensioner was disclosed by the Japanese Utility Model Application Laid-open No. 62-19015 as shown in the FIG. 10. The conventional belt tensioner principally comprises a cylindrical casing 1 to be fixed on equipment by means of holes formed on a the wing portion thereof, a rotational cylinder 2 rotatably inserted in the casing 1, a tension rod 3 urged by the rotating operation of the rotational cylinder 2 engaged with male threads formed on the front portion of the rotational cylinder 2, a torsion spring 4 for driving the rotational cylinder 2 and a bearing 5 for supporting the tension rod 3 and at the same time for restricting rotational movement of the tension rod 3 by means of a non circular bearing.
When the tension rod 3, wherein a rotational energy of torsion spring is stored by turning the rotational cylinder 2, abuts on a belt or chain, the tensions the rod 3 tenses belt or chain by an urging force converted from rotational energy of the torsion spring 4. That is, since the rotation of the tension rod 3 is restricted by the bearing 5, the rotational energy of rotational cylinder 2 is converted into an urging energy for tensioning the belt or chain. In this manner, the chain or belt can be tensioned without excessive play, but constant tension.
In FIG. 10, numeral 7 shows a seal bolt screwed in the rear end of casing 1 and numeral 6 shows a boot covering the tension rod 3 and the front end of casing 1.
In this case, the tension rod 3 has to be locked during mounting on equipment or transport. Accordingly, a holder 10' of which lower ends are inserted in the neck of casing 1' is used for. The holder 10 locks the outward movement of tension rod 3 by holding tension head 3a.
The tension head 3a of the tension rod 3 is of flat head. However, when the tensioner is used for tensioning directly or indirectly on the belt or chain, it is possible that the flat head 3 interferes the endless movement of the belt or chain. Therefore, the flat head 3a of tension rod 3 is rounded commonly. However, if it is planned to use such holder as shown in FIG. 10, there may occur a problem that the holder 10 slips off from the rounded head of tension rod 3 releasing the tension rod 3.
Then, the object of the present invention is to provide such tensioner that the rounded head of the tension rod may be locked firmly.